I would start by searching these forums or google for a combination of the words xorg, glx, and the name of your video card manufacturer (I.E. ati, nvidia, intel). You should find plenty of things to get you started.

If you do not, please post back here with the result of the command lspci, and your /etc/X11/xorg.conf file. Other useful pieces of information for tracking down video problems are what specific graphics card/chipset you've got, and any warnings or errors that you might find in your xorg logs: grep -E 'WW|EE' /var/log/Xorg.0.log